Add coverage report with codecov

[aio-libs]

Add coverage report with codecov

[achimnol]

Yes, that's the my next plan. 😉

[achimnol]

Hmmm, I cannot get it uploading the correct report to codecov.io.
Surely it generates the report at .coverage file on the container's working directory which is mounted from the working copy of the Travis CI instance, but it seems to be uploading an empty report.

In my local docker-compose test, I get:

aiodocker_1  | tests/test_integration.py .....x....
aiodocker_1  |
aiodocker_1  | ----------- coverage: platform linux, python 3.6.1-final-0 -----------
aiodocker_1  | Name                       Stmts   Miss  Cover
aiodocker_1  | ----------------------------------------------
aiodocker_1  | aiodocker/__init__.py          2      0   100%
aiodocker_1  | aiodocker/channel.py          19      0   100%
aiodocker_1  | aiodocker/constants.py         1      0   100%
aiodocker_1  | aiodocker/docker.py          365    130    64%
aiodocker_1  | aiodocker/exceptions.py        9      2    78%
aiodocker_1  | aiodocker/jsonstream.py       28      1    96%
aiodocker_1  | aiodocker/multiplexed.py      31      4    87%
aiodocker_1  | aiodocker/utils.py            37     20    46%
aiodocker_1  | ----------------------------------------------
aiodocker_1  | TOTAL                        492    157    68%
aiodocker_1  |
aiodocker_1  |
aiodocker_1  | ===================== 9 passed, 1 xfailed in 44.71 seconds =====================
aiodocker_aiodocker_1 exited with code 0

I even see .coverage file on the host working copy after finishing docker-compose tests.
Do you have any ideas on this...?

[achimnol]

Thanks to @gaopeiliang, we now have the working code coverage report! (fixed via #19)